Fast Five Quiz: Refresh and Test Your Knowledge of Myasthenia Gravis

Amy Kao, MD

Disclosures

July 06, 2021

The following maneuvers are helpful for diagnosis of MG:

  • Sustained upgaze (60-180 seconds): results in fatigable ptosis in one or both eyes.

  • Manual elevation of the more ptotic lid may worsen ptosis of the contralateral eyelid, a phenomenon known as "enhanced ptosis." This phenomenon is based on the Hering law of equal innervation.

  • Sustained tight closure of the eyelids can induce fatigue of the orbicularis oculi muscles resulting in the white sclera of the eye slowly becoming apparent under the partially open eye. This is called the "peek sign."

  • Fatigable diplopia in sustained lateral gaze (60 seconds): results in diplopia with images appearing side by side.

  • Sustained abduction of the arms (120 seconds): patient can no longer hold arms up, or weakness becomes apparent with subsequent manual testing.

  • Ask the patient to perform deep knee bends with the back straight. The patient's palm is held in that of the examiner. An increase in pressure against the examiner's palm while doing this maneuver is an early sign of weakness. Also, a forward lean by the patient (moving the center of gravity forward) is another sign of weakness.

  • Counting aloud (1-50): enhances dysarthria (nasal, lingual, or labial) and results in dyspnea. Patient may sound relatively clear on speaking initially but will become increasingly dysarthric to the point of becoming unintelligible.

  • Weakness of the laryngeal muscles results in hoarseness. This can be elicited by asking the patient to make a high-pitched ("eeee") sound.

  • Single-breath counting aloud (1-20) may elicit not only dysarthria but dyspnea and gives an approximate idea of the vital capacity. Multiplying the number the patient can achieve with one breath by 100 (eg, 20 ´ 100 = 2000 cc) will provide a reasonable estimate of the vital capacity.

  • Sustained elevation of leg while lying supine (90 seconds): Patient can no longer hold leg up, or weakness becomes apparent with subsequent manual testing.

  • Repeated arising from chair without use of arms (up to 20 repetitions): Patient fatigues after several attempts. Early/mild weakness may cause exaggerated lean-forward and ''buttocks-first'' maneuver.

Learn more about the evaluation of MG.

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